No video this time, as this was supposed to be a 1-hour job… that ended up on the back burner with all the other projects for 3 months. Paying customers come first…
This is a Quad CD99-II, a friend asked me to check why it no longer read discs. Apparently it had been reading only about half of them for a while, and when that symptom was ignored, it had stopped altogether. Continue reading
In the early 90s Philips were at the top of their game when they introduced the DSS930, a digital-input only, active DSP loudspeaker far ahead of its time. We got our hands on a pair, investigate the design and the state of these classics and discover a design flaw that has gone unnoticed for 30 years.
After building the CNC machine in part 1, we test it by milling a single sided PCB.
Can you guess what part 3 will be about?
Remco loses his mind and buys a CNC
Fire in the disco
Two posts in one year? Is the world ending? Well, yes, but not just today.
I’ve been visited by a pair of handsome Bose 1800 amps over the past weeks. They needed a DC output delay / DC protection relays because apparently that tech did not yet exist in the mid 1970s. Those solid state devices were still a bit scary, I suppose. Continue reading
Yes, I am still alive. Sort of. 🙂
This should involve only about 3 people in the world, but hey, I should blog more even if the relevance is negligible. If this helps 1 person, I’m glad.
Not recently at all I bought a bunch of Yokogawa A1D03B supplies from Pollin (originally meant for HP printers). The idea was that they are nice to supply small / medium amplifiers for active loudspeakers. The output is 31.6V but I needed about 24V.
About four and a half thousand years ago, I designed (SA)CD player output stages with vacuum tubes and at some point came up with a transistor version, called the SACDenhancer.
Original version, ca. 2003 AD
In double blind tests this was a big preference over the built-in opamp solution. It spawned off a plethora of discrete output stages from various manufacturers and modification shops that were all the rage in the day. I had some pretty good spectrum analyzer but never could find definitive measurable differences between the standard output stage and this one.
Fast forward 15 years and I’m still getting requests for this design, so I had a PCB made. Both fabrication and measurement capabilities have moved quite a bit forward in the meantime.
Reboot, ca. 2016 AD. How nice you can now get solder mask in ‘UltrAnalog’ colour palette from China.
This version follows the original schematic but adds a second output stage for fully differential processing. As such the schematic stays ridiculously simple – just a long-tailed input stage and emitter follower output. Couldn’t be simpler (I tried. Believe me. It wasn’t good).
Test conditions unless otherwise specified – 1V rms differential, 997 Hz input, AES17 measurement filter, unweighted
THD+N : -99 +/- 0.5 dB
Best THD : 109 dB @ 0.7Vrms input
SNR: 100 +/- 2 dB
Frequency response linearity: +/- 0.02 dB, 20 Hz – 20 kHz
Gain linearity: +/- 0.025 dB
THD+N vs. Freq
THD vs Level
Crosstalk
Intermodulation, 1k sine 1:1 with swept sine from 60 kHz to 6 kHz
Good news – the performance indicators are all green: no defects. This is pretty much as well-behaved as you might expect from a discrete design. But while it clearly says there’s nothing wrong with how this will sound, it does not prove it will sound better than an opamp either.
So let’s pit this thing against an opamp stage and see what happens. In the left corner, representing the heavyweight class, the Analog Devices OPA275. The challenging contestant, some ridiculous discrete design from some dude in 2003 thinking they know better. All that and more, in part 2…
WM8804 application board (eBay) modified to output CLKOUT pin (yellow-black wire)
Recently I needed a special type of I2S signal, namely a 4 signal set of DATA, BCLK, FCLK and also an MCLK of 49.152 MHz.
Many modern DACs, DSPs and digital power amplifiers need this high clock frequency. And of course you would want this signal to be synchronous to the Frame Clock such that the converter has a fixed number of MCLK per FCLK cycles so as to minimize jitter.
Many S/PDIF receivers implement a fixed clocking in hardware mode which limits your options and flexibility, so it is worth exploring software control. It is really not so hard. Continue reading
There is one thing the older Audio Precision System One and Twos don’t have which can be quite annoying: they don’t have USB host functionality. And given that all the processing and clocking happens inside the unit, the control software can’t reroute the digital signal generator to a USB output.
Tenor T7022, an often-encountered USB receiver. Does it do bit correct feed-through?
Of course you can use a PC to feed the USB sound card and measure the output with the AP, but then you don’t have the generator signal to do e.g. sweeps or automation. The best of course would be to somehow get to a full loop starting at the AP signal generator back to the analyzer. After quite a lot of tinkering, I managed to do just that.
